Simply put, Oda's fault. All characters have a certain purpose. Chopper's medically based. Only natural people will view him more from a medical stand-point than a combat-based stand-point. If people aren't interested in medicine or such areas or even his story line, they're likely not going to be interested in him.
It's no different to Nami, no one views her as a combat orientated character, but a character who is based on navigation and meteorology. Chopper's story and ambition is medical.
End of the day, people appeal more to combat, Chopper's simply not combat orientated.
You can't criticise people for not wanting to talk about a character they don't like or a character they're not interested in. Just because you like Chopper doesn't mean others should like Chopper. We're all individuals and that means we like different things. It just so happens you're a minority and that's just the way it is.
If Oda makes Chopper more interesting, then they'll talk more about him, until then, there's really nothing wrong about him not being discussed much. It's simply a matter of preference and what appeals to people; I can't tell you what to like and neither should you try to tell people what they should like.
There's nothing to try to understand about why people don't talk about Chopper. The reason is simple, they just don't find him interesting. No different to loving Opera music or Classical, there's nothing to understand about people who don't find Opera music or Classical appealing, it's simply down to their taste and preference. Even more relatable, you like One Piece and there are people who don't like One Piece or Anime or Manga, why? They simply don't, it's not to their taste.